placed near a tendril, the terminal branches wind quite round it, and
then seize their own lower branches or the main stem. The stick is
thus firmly, but not neatly, grasped. What the tendrils are really
adapted for, appears to be such objects as the thin culms of certain
grasses, or the long flexible bristles of a brush, or thin rigid
leaves such as those of the Asparagus, all of which they seize in an
admirable manner. This is due to the extremities of the branches
close to the little hooks being extremely sensitive to a touch from
the thinnest object, which they consequently curl round and clasp.
When a small brush, for instance, was placed near a tendril, the tips
of each sub-branch seized one, two, or three of the bristles; and
then the spiral contraction of the several branches brought all these
little parcels close together, so that thirty or forty bristles were
drawn into a single bundle, which afforded an excellent support.
POLEMONIACEAE.--Cobaea scandens.--This is an excellently constructed
climber. The tendrils on a fine plant were eleven inches long, with
the petiole bearing two pairs of leaflets, only two and a half inches
in length. They revolve more rapidly and vigorously than those of
any other tendril-bearer observed by me, with the exception of one
kind of Passiflora. Three large, nearly circular sweeps, directed
against the sun were completed, each in 1 hr. 15 m.; and two other
circles in 1 hr. 20 m. and 1 hr. 23 m. Sometimes a tendril travels
in a much inclined position, and sometimes nearly upright. The lower
part moves but little and the petiole not at all; nor do the
internodes revolve; so that here we have the tendril alone moving.
On the other hand, with most of the species of Bignonia and the
Eccremocarpus, the internodes, tendrils, and petioles all revolved.
The long, straight, tapering main stem of the tendril of the Cobaea
bears alternate branches; and each branch is several times divided,
with the finer branches as thin as very thin bristles and extremely
flexible, so that they are blown about by a breath of air; yet they
are strong and highly elastic. The extremity of each branch is a
little flattened, and terminates in a minute double (though sometimes
single) hook, formed of a hard, translucent, woody substance, and as
sharp as the finest needle. On a tendril which was eleven inches
long I counted ninety-four of these beautifully constructed little
hooks. They readily catch soft wood, or gloves, or the skin of the
naked hand. With the exception of these hardened hooks, and of the
basal part of the central stem, every part of every branchlet is
highly sensitive on all sides to a slight touch, and bends in a few
minutes towards the touched side. By lightly rubbing several sub-
branches on opposite sides, the whole tendril rapidly assumed an
extraordinarily crooked shape. These movements from contact do not
interfere with the ordinary revolving movement. The branches, after
becoming greatly curved from being touched, straighten themselves at
a quicker rate than in almost any other tendril seen by me, namely,
in between half an hour and an hour. After the tendril has caught
any object, spiral contraction likewise begins after an unusually
short interval of time, namely, in about twelve hours.
Before the tendril is mature, the terminal branchlets cohere, and the
hooks are curled closely inwards. At this period no part is
sensitive to a touch; but as soon as the branches diverge and the
hooks stand out, full sensitiveness is acquired. It is a singular
circumstance that immature tendrils revolve at their full velocity
before they become sensitive, but in a useless manner, as in this
state they can catch nothing. This want of perfect co-adaptation,
though only for a short time, between the structure and the functions